WO1996023151A1

WO1996023151A1 - Improved fluid pressure activated piston return spring seal

Info

Publication number: WO1996023151A1
Application number: PCT/US1995/015755
Authority: WO
Inventors: John A. Burke
Original assignee: Greene Tweed of Delaware Inc
Current assignee: Greene Tweed of Delaware Inc
Priority date: 1995-01-23
Filing date: 1995-12-05
Publication date: 1996-08-01
Anticipated expiration: 1997-07-23
Also published as: AU4373896A

Abstract

An improved fluid pressure activated piston return spring seal element for installation in an annular groove in a piston housing is disclosed. The annular groove has first and second radial side walls, an axial base wall, and a mouth. The seal includes an annularly shaped element which in toroidal cross section has first (24) and second (40) oppositely situated radial faces and an axial face (42). The first radial face (24) defines a pressure side of the element, and includes a notch (26) extending inwardly with respect to the element and a base wall pressure sealing lip (28). The axial face (42) partially protrudes through the mouth of the groove and has a piston pressure sealing lip (44), a first angled surface (48) extending from the piston pressure sealing lip at a first angle to an intermediate point (50), and a second angled surface (52) extending from the intermediate point at a second angle larger than the first angle toward the second radial face (40). When the seal element is installed in the groove, the piston pressure sealing lip is outside the groove and proximate the first radial face and the intermediate point is proximate the mouth of the groove. The piston pressure sealing lip and the piston move from a relaxed to a pressurized position when sufficient fluid pressure is applied to the pressure side, and return to the relaxed position when the fluid pressure is removed.

Description

IMPROVED FLUID PRESSURE ACTIVATED PISTON RETURN SPRING SEAL

Background of the Invention

The present invention relates generally to spring seals, and more particularly, to an improved fluid pressure activated piston return spring seal that may be employed in a disc brake braking system to achieve increased piston bore stroke.

In disc brake braking systems, pressure is typically applied to a piston by way of a braking fluid and the piston moves a brake lining into contact with a brake disc to retard rotational movement. As should be understood, it is necessary to provide a biasing device to return the piston and the brake lining from the pressurized braking position to a relaxed position. As can be seen from U.S. Patents Nos. 4,229,013 and 4,342,463, hereby incorporated by reference, it is known to provide a spring seal assembly having a sealing element which seals the braking fluid, which grips the piston and becomes deflected when the piston and spring seal assembly are pressurized by the fluid, and which retracts the piston when the fluid pressure is removed. Accordingly, the piston and the associated lining are withdrawn a sufficient distance to prevent the lining from remaining in contact with the brake disc and to allow free rotational movement.

However, a spring seal assembly as described in the aforementioned references has a serious disadvantage in that the deflection of the seal element and the resultant stroke of the piston are limited. More specifically, since the seal element in toroidal cross-sectional has a generally planar pressure side or face, the maximum deflection of the seal element and the resultant maximum bore stroke of the piston is approximately ten percent (10%) of the seal cross- section, a value too small to meet performance requirements under some circumstances. In an effort to increase the seal element deflection and piston stroke of the aforementioned spring seal assembly, the dimensions of the seal element in toroidal cross-section were proportionally increased. However, the increased size seal element required increased fluid pressure for full deflection operation and otherwise did not provide adequate increased deflection and piston stroke.

A need exists, then, for a spring seal assembly having a seal element with increased deflection and providing increased piston stroke while still maintaining a reliable seal. More particularly, a need exists for a spring seal assembly having a seal element with a toroidal cross-sectional shape that allows the piston and the pressure sealing lip of the seal element to deflect under pressure from an originating unpressurized position a relatively large distance of about 0.1 inches or more and still return to the originating position when the pressure is removed.

Summary of the Invention

The aforementioned need is satisfied by an improved fluid pressure activated piston return spring seal element for installation in an annular groove in a piston housing. The annular groove has in toroidal cross-section first and second generally parallel radial side walls, an axial base wall extending between the first and second side walls, and a mouth. The seal element has a generally annular shape and is formed of an elastomeric material.

More specifically, the seal element has a toroida cross-section which includes first and second oppositely situated radial faces and an axial face. The first radial face faces the first side wall, defines a pressure side of the seal element, and includes a notch extending inwardly with respect to the seal element and a base wall pressure sealing lip for sealingly engaging the base wall. The axia face faces toward and partially protrudes through the mouth of the groove, and has a piston pressure sealing lip for sealingly engaging a piston positioned in the housing and across the mouth of the groove. A first angled surface extends from the piston pressure sealing lip at a first angle with respect to the axis of the element and in a direction generally toward the second radial face to an intermediate point. When the seal element is installed in the groove, the piston pressure sealing lip is outside the groove and proximate the first radial face and the intermediate point is proximate the mouth of the groove. A second angled surface extends from the intermediate point at a second angle with respect to the axis of the element larger than the first angle and in a direction generally toward the second radial face.

Accordingly, the piston pressure sealing lip and the piston move from a relaxed position to a pressurized position when sufficient fluid pressure is applied to the pressure side, and return from the pressurized position to the relaxed position when the fluid pressure is removed.

Brief Description of the Drawings

The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:

Fig. 1 is a toroidal cross-sectional view of a seal element employed in a first embodiment of a spring seal assembly;

Fig. 2 is a toroidal cross-sectional view of the seal element shown in Fig. 1 positioned within a seal gland and compressed by a piston extending across the mouth of the gland to form the spring seal assembly;

Fig. 3 is a view similar to Fig. 2 showing the spring seal assembly under pressure; Fig. 4 is a toroidal cross-sectional view of a first and second seal element employed in a second embodiment of a spring seal assembly;

Fig. 5 is a toroidal cross-sectional view of the first and second seal elements shown in Fig. 4 positioned within a seal gland and compressed by a piston extending across the mouth of the gland to form the spring seal assembly; and

Fig. 6 is a view similar to Fig. 5 showing the spring seal assembly under pressure.

Detailed Description of Preferred Embodiments

Certain terminology may be used in the following description for convenience only and is not limiting. The words "left", "right", "upper" and "lower" designate directions in the drawings to which reference is made. The words "inwardly" and "outwardly" are further directions toward and away from, respectively, the geometric center of the referenced element . The terminology includes the words above specifically mentioned, derivatives thereof, and words of similar import . Referring to the drawings in detail, wherein like numerals are used to indicate like elements throughout, there is shown in Fig. 1 a seal element 10 constructed in accordance with a first embodiment of the present invention. As should be understood, the seal element 10 is annularly shaped and is formed from an elastomeric material.

Preferably, the elastomeric material comprises a rubber material, although it will be recognized that other materials such as polymeric plastic may be employed without departing from the spirit and scope of the present invention. As previously stated, a disc brake represents a typical environment in which the seal element 10 of the present invention may be incorporated to form a spring seal assembly 11 (as seen in Fig. 2) . The brake is conventional and per se forms no part of the present invention. A general description of the disc brake may be found in either of U.S. Patents Nos. 4,229,013 or 4,342,463.

Referring now to Fig. 2, it may be seen that the spring seal assembly 11 includes a piston housing 12 having a seal gland or groove 14. More particularly, the groove 14 has in toroidal cross-section first and second generally parallel radial side walls 16, 18, and an axial base wall 20 that extends between the first and second side walls 16, 18. The groove 14 is generally open and has a mouth 22 opposite the base wall 20.

With reference to Figs. 1 and 2, the seal element 10 has a first radial face 24 that faces toward the first side wall 16 when the seal element 10 is positioned within the groove 14. The first radial face 24 is the pressure side of the seal element 10 and accordingly when employed in a disc brake braking system is exposed to fluid pressure from a braking fluid (not shown) . As should be understood, the braking fluid may typically be a gas such as compressed air or a liquid such as hydraulic brake fluid, hydraulic oil, or conventional engine oil. However, it will be recognized that other fluids such as water may be employed without departing from the spirit and scope of the present invention.

The first radial face 24 of the seal element 10 has a notch 26 extending into the seal element 10.

Preferably, the first radial face includes first and second generally flat, radial surfaces 30, 32, one on either side of the notch 26. The notch 26 is defined by a first angled portion 34 that extends from the first radial surface 30 into the seal element 10 to a generally inwardly rounded crotch 36 at the innermost portion of the notch 26, and a second angled portion 38 that extends from the second radia surface 32 into the seal element 10 to the rounded crotch 36. Preferably, and as seen in Fig. 1, when the seal element 10 is not installed within the groove 14 and is not compressed by the piston 46, the first and second angled portions 34, 38 respectively extend at angles γ, δ with respect to a line running perpendicular to the axis 45 of the seal element 10. Typically, the angle γ ranges between about 30 and 60 degrees and the angle δ ranges between abou 50 and 70 degrees, although it is preferable that angle γ b about 45 degrees and that angle δ be about 60 degrees.

The first radial face 24 also has a base wall pressure sealing lip 28 that sealingly engages the base wal 20 to seal the fluid and prevent the fluid from moving past the seal element 10 along the base wall 20. As seen in Fig 1, the base wall pressure sealing lip 28 and the second angled portion 38 of the notch 26 form a static leg 39. Preferably, and as seen in Fig. 2, the static leg 39 juts toward the first side wall 16 and sealingly engages the bas wall 20 of the groove 14 when the seal element 10 is installed in the groove 14. Also preferably, when the seal element 10 is compressed by the piston 46, the compression increases the sealing engagement of the static leg 39 with the base wall 20 and causes the static leg 39 to bend towar the mouth 22 of the groove 14.

The seal element 10 also has a second radial face 40 opposite the first radial face 24 and facing the second side wall 18. Preferably, and as seen in Fig. 2, the secon side wall 18 extends a distance D_α from the base wall 20 to the mouth 22 of the groove 14, and the second radial face 4 extends a distance D₂ from the base wall 20 toward the mouth 22 of the groove 14, such that the distance D₂ is approximately one-quarter the distance D_x. Accordingly, the second radial face 40 of the seal element 10 engages the second side wall 18 of the groove 14 and stabilizes the sea element 10 during pressurization and deflection. The seal element 10 also has a generally axial surface 41 extending between the second radial face 40 and the static leg 39 to aid in stabilizing the seal element 10 during pressurization and deflection. As seen in Figs. 2 and 3, the axial surface 41, is adjacent the base wall 20 when the seal element 10 is compressed by the piston 46 and is moved into substantially complete contact with the base wall 20 when sufficient fluid pressure (P) is applied. The seal element 10 has an axial face 42 that faces toward and partially protrudes through the mouth 22 of the groove 14 (as seen in Fig. 2) . The axial face 42 has a piston pressure sealing lip 44 that engages a piston 46 positioned within the housing 12 and across the mouth 22 of the groove 14. More particularly, the piston pressure sealing lip 44 sealingly engages the piston 46 to prevent sealing fluid from moving past the seal element 10 along the piston 46, and grips and moves with the piston 46 when the piston 46 and the seal assembly 11 are pressurized. As seen in Fig. 1, the piston pressure sealing lip 44 and the first angled portion 34 of the notch 26 form a dynamic leg 47. Preferably, the dynamic leg 47 juts toward the first side wall 16 and out of the mouth 22 of the groove 14 when the seal element 10 is installed in the groove 14. Also preferably, when the seal element 10 is compressed by the piston 46, the compression causes the dynamic leg 47 to bend toward the base wall 20 of the groove 14.

As best seen in Fig. 1, the axial face 42 has first and second angled surfaces 48, 52. The first angled surface 48 extends from the piston pressure sealing lip 44 in a direction toward the second radial face 40 and to an intermediate point 50. Particularly when the seal element 10 is not installed within the groove 14 and is not compressed by the piston 46, the first angled surface 48 extends at an angle x with respect to a line parallel to the axis 45 of the seal element 10. Typically, the angle α ranges between about 5 and 15 degrees, although it is preferable that angle a be about 10 degrees.

As seen in Fig. 2, the piston pressure sealing l 44 is outside the groove 14 and is proximate the first radial face 24 of the seal element 10, and the intermediat point 50 is proximate the mouth 22 of the groove 14. Accordingly, when the seal element 10 is positioned within the groove 14 and the piston 46 compresses the seal elemen 10 toward the base wall 20 of the groove 14, the first angled surface 48 substantially completely contacts the piston 46 and grips the piston 46 along with the piston pressure sealing lip 44, and the dynamic and static legs 4 39 are forced toward one another to decrease the toroidal cross-sectional area of the notch 26. Referring again to Fig. 1, the second angled surface 52 of the axial face 42 extends from the intermediate point 50 and in a direction generally toward the second radial face 40. Particularly when the seal element 10 is not installed within the groove 14 and is no compressed by the piston 46, the second angled surface 52 extends at a second angle β with respect to a line parallel to the axis 45 of the seal element 10. Preferably, and as seen in Fig. 2, when the seal element 10 is positioned within the groove 14 and the piston 46 compresses the seal element 10 toward the base wall 20 of the groove 14, the angle β does not appreciably change. Typically, the angle ranges between about 60 and 80 degrees, although it is preferable that angle β be about 70 degrees.

In the first preferred embodiment of the present invention, and as seen in Fig. 2, the second angled surface 52 extends from the intermediate point 50 to the second radial face 40, and the juncture of the second angled surface 52 and the second radial face 40 is adjacent the second side wall 18. As may be seen, then, a generally wedge-shaped spring gap 54 opening toward the mouth 22 of the groove 14 is formed between the second angled surface 52 and the second side wall 18.

As seen in Fig. 3, when sufficient fluid pressure (P) is applied to the pressure side or first radial face 24 of the seal element 10, the piston pressure sealing lip 44 is moved or deflected by the fluid pressure (P) from a relaxed position (as shown in Fig. 2) to a pressurized position (as shown in Fig. 3) , the spring gap 54 substantially closes, the second angled surface 52 substantially completely contacts the second side wall 18, and the elastomeric material that forms the seal element 10 becomes spring-loaded. Accordingly, since the piston pressure sealing lip 44 and the first angle surface 48 are gripping the piston 46, the piston 46 is also moved from a relaxed position to a pressurized position.

When the fluid pressure (P) is removed, the spring-loaded elastomeric material returns to an unloaded shape according to the memory of the material, the spring gap 52 re-opens and the piston pressure sealing lip 44 and the piston 46 return from the pressurized position of Fig. 3 to the relaxed position of Fig. 2. As should be understood, the amount of deflection of the piston pressure sealing lip 44 and the corresponding stroke of the piston 46 during a pressurization / de-pressurization cycle is substantially equal to the distance D₃ from the intermediate point 50 to the juncture of the second side wall 18 and the mouth 22 of the groove 14 (as seen in Fig. 2) .

It may be appreciated that the amount of deflection and stroke that may be achieved by the seal assembly 11 and the piston 46 is dependent upon the shape of the groove 14, the notch 26, and the spring gap 54, the angle a of the first angled surface 48, the second angle β of the second angled surface 52, and the amount of fluid pressure applied against the pressure side of the seal element 10, among other things. Moreover, the type and flexibility of the material employed to construct the seal element 10 and the various linear dimensions of the seal element 10 also contribute to the amount of deflection and piston stroke achievable.

As an example, it has been found that a 0.1 inch deflection and piston stroke may be achieved with a groove 14 that is 0.47 inches wide and 0.375 inches deep (distance D ; with a seal element 10 constructed of nitrile elastomer and having an angle a of 10 degrees, an angle β of 70 degrees, and a spring gap distance D₃ of 0.105 inches; and with a notch 26 in the seal element 10 having angles γ, δ of 45 and 60 degrees, respectively, and a rounded crotch 36 that is about 0.16 axial inches within the notch 26 and 0.2 radial inches from the base wall pressure sealing lip 28, when such a seal assembly 11 is pressurized to about 1,500 PSI.

The axial face 42 of the seal element 10 may also have a third angled surface 56 (as best seen in Fig. 1) extending from the piston pressure sealing lip 44 in a direction generally toward the first radial face 24. As may be understood, the third angled surface 56 is useful under certain circumstances as an assembly lead-in chamfer. However, the third angled surface 56 is not necessary for assembly insertion of a conventional piston and may actually be undesirable under other circumstances. If undesirable or unnecessary, the third angled surface 56 may be deleted by extending the first angled surface 48 and the first radial surface 30 to meet at the piston pressure sealing lip 44.

Referring now to Figs. 4-6, there is shown first and second seal elements 60, 66 of a spring seal assembly 58 constructed in accordance with a second preferred embodiment of the present invention. As may be seen, the first element 60 is substantially similar to the seal element 10 of the first embodiment of the present invention. However, the first element 60 differs from the seal element 10 in that the first element 60 also includes a generally inwardly curved portion 62 extending from the second angled surface 52 toward the second radial face 40. Accordingly, the rounded surface 62 and the second radial face 40 define a pedestal 64.

Preferably, the second element 66 is generally annularly shaped, is formed of a non-elastomeric anti- extrusion material, and has an axis 67 generally coinciding with the axis 45 of the first element 60. The second element 66 is an anti-extrusion ring and is positioned generally within the groove 14 on the pedestal 64 and between the second angled surface 52 and a portion of the second side wall 18 adjacent the mouth 22 of the groove 14. The second element 66 may have a generally rectilinear shape in toroidal cross-section. Preferably, the second element 66 has a generally outwardly curved portion 70 that is complementarily received by the rounded surface 62.

Preferably, the anti-extrusion ring or second element 66 is formed from a non-elastomeric material such as polytetrafluoroethylene (PTFE) thermoplastic or nylon plastic. However, one skilled in the art will recognize that other non-elastomeric materials such as polyetheretherketone (PEEK) thermoplastic may be employed without departing from the spirit and scope of the present invention.

As should be understood, the second element or anti-extrusion ring 66 is employed when high pressure above approximately 1,500 PSI is applied to the spring seal assembly 58. Normally, a liquid sealing fluid such as ABF brake fluid is employed to exert such high pressure. As seen in Fig. 5, when the first and second elements 60, 66 of the spring seal assembly 58 are positioned within the groove 14, the piston 46 is positioned across the mouth 22 of the groove 14, and the first and second elements 60, 66 are not pressurized, the second element 66 preferably does not contact the piston 46 in an interference fit. When pressure (P) is applied, as seen in Fig. 6, the pressure (P) causes the pedestal 64 to exert a generally radial force against the anti-extrusion ring 66 and the ring 66 sealingly contacts the piston 46. Accordingly, the anti-extrusion ring 66 prevents the first element 60 from being extruded through the gap between the piston 46 and the housing 12 under the force of the high pressure (P) .

As with the first embodiment of the present invention, the second embodiment preferably has a generally wedge-shaped spring gap 72 (as seen in Fig. 5) . However, the spring gap 72 in the second embodiment is formed between the second element 66 and the second angled surface 52 of the first element 60. Like the spring gap 54 in the first embodiment, the spring gap 72 substantially closes when a sufficient fluid pressure (P) is applied at the first radial face or pressure side 24 of the first element 60 (Fig. 5) and reopens when the fluid pressure (P) is removed (Fig. 6) . In all other material aspects, the spring seal assembly 58 of the second embodiment of the present invention operates in the same manner as the spring seal assembly 11 of the first embodiment . With either embodiment of the present invention, a separate piston return spring is not required and the groove 14 is a standard seal groove requiring no special machining or shape. The spring seal assembly 11 or 58 of the present invention may be employed as a male or female seal assembly so long as the assembly is stationary with respect to the piston housing 12.

From the foregoing description, it can be seen that the present invention comprises an improved fluid pressure activated piston return spring seal element for installation in a piston housing comprising an annular groove. It will be recognized by those skilled in the art that changes may be made to the above-described embodiments of the invention without departing from the broad inventive concepts thereof. It is understood, therefore, that this invention is not limited to the particular embodiment disclosed, but is intended to cover all modifications which are within the spirit and scope of the appended claims.

Claims

1. An improved fluid pressure activated piston return spring seal element for installation in a piston housing comprising an annular groove having in toroidal cross-section first and second generally parallel radial side walls, an axial base wall extending between the first and second side walls, and a mouth, the spring seal element being formed of an elastomeric material and having a generally annularly shape and an axis, the element further having in toroidal cross-section: a first radial face for facing the first side wall, the first radial face defining a pressure side of the element and including a notch extending inwardly with respect to the element and a base wall pressure sealing lip for sealingly engaging the base wall; a second radial face situated opposite the first radial face for facing the second side wall; and an axial face for facing toward and partially protruding through the mouth of the groove, the axial face including: a piston pressure sealing lip for being outside the groove and sealingly engaging a piston positioned in the housing and across the mouth of the groove, the piston pressure sealing lip being proximate the first radial face; a first angled surface extending from the piston pressure sealing lip in a direction generally toward the second radial face to an intermediate point, the first angled surface extending at a first angle with respect to the axis of the element, the intermediate point for being proximate the mouth of the groove; and a second angled surface extending from the intermediate point in a direction generally toward the second radial face, the second angled surface extending at a second angle with respect to the axis of the element, the second angle being larger than the first angle, the piston pressure sealing lip and the piston moving from a relaxed position to a pressurized position when sufficient fluid pressure is applied to the pressure side, the piston pressure sealing lip and the piston returning from the pressurized position to the relaxed position when the fluid pressure is removed.

2. The spring seal element as recited in claim 1 wherein the first radial face has first and second generally radial surfaces, the notch being situated between the first and second radial surfaces and comprising a first angled portion extending inwardly with respect to the element from the first radial surface and a second angled portion extending inwardly with respect to the element from the second radial surface, the first and second angled portions meeting at a generally inwardly rounded surface.

3. The spring seal element as recited in claim 1 further comprising a third angled surface extending from the piston pressure sealing lip in a direction generally toward the first radial face.

4. The spring seal element as recited in claim 1 wherein the second side wall extends a first distance from the base wall to the mouth of the groove, and wherein the second radial face extends a second distance from the base wall toward the mouth of the groove, the second distance being approximately one-quarter the first distance.

5. The spring seal element as recited in claim 1 wherein the element is a first element and is in combination with a second generally annularly shaped element formed of a non-elastomeric material and having an axis generally coinciding with the axis of the first element, the second element for being positioned generally within the groove and between the second angled surface and a portion of the second side wall.

6. The spring seal element as recited in claim wherein the first element further includes a generally inwardly curved portion extending from the second angled surface toward the second radial face, and wherein the second element has a generally outwardly curved portion fo being complementarily received by the generally inwardly curved portion.

7. The spring seal element as recited in claim wherein the second element and the second angled surface form a spring gap therebetween, the spring gap substantial closing when sufficient fluid pressure is applied to the pressure side and re-opening when the fluid pressure is removed.

8. The spring seal element as recited in claim wherein the second angled surface extends from the intermediate point to the second radial face, the second angled surface and the second side wall forming a spring ga therebetween, the spring gap substantially closing when sufficient fluid pressure is applied to the pressure side and re-opening when the pressure is removed.